Get access

A quantitative approach to sedimentary surface structures contoured by the interplay of microbial colonization and physical dynamics

Authors

  • Nora Noffke,

    1. Carl von Ossietzky University Oldenburg, Marine Laboratory of the Institute for Chemistry and Biology of the Marine Environment (ICBM), Schleusenstr. 1, 26382 Wilhelmshaven, Germany,
    Search for more papers by this author
    • Wolfgang E. Krumbein

      1. Carl von Ossietzky University Oldenburg, Institute for Chemistry and Biology of the Marine Environment (ICBM), PO Box 2503, 26111 Oldenburg, Germany
      Search for more papers by this author

    Abstract

    In the tidal flats of Mellum Island (southern North Sea), biofilms and microbial mats, generated largely by cyanobacteria, colonize the sedimentary surfaces. Biostabilization effects and biomass enrichment influence erosional and depositional dynamics resulting from tidal flushing and storm surges. The overlapping of both biological and physical forces causes the development of characteristic sedimentary structures. To obtain a quantitative expression of the degree of effectiveness of microbial colonization in the formation of structures in an extended tidal area, a modification index (MOD-I) was developed based on the following values: (i) the proportion of mat-covered area related to a defined investigation area (IA); (ii) the degree of steepness of slope angles of raised erosional remnants (IS); and (iii) the degree of microbial levelling of a rippled sedimentary surface (IN). The MOD-I was calculated for several defined regions within the study area, and both winter and summer situations were considered. The MOD-I values show, first, that the lower intertidal zone is characterized by index values approaching zero. This implies that microbially induced effects in this zone are negligible, even in summer. Second, the upper intertidal zone is characterized by lower index values in winter and relatively high values in summer. This implies a predominantly seasonal control on the biofilm development in this zone. Third, in the lower supratidal zone, the index values are almost identical during both winter and summer. This implies non-seasonal biological effects in this zone. Concomitant empirical studies on the composition of microbial mats and films suggest that the dominant microbial type influences the MOD-I value.

    Get access to the full text of this article

    Ancillary